Optical information recording method, optical information recording and reproducing device, and optical information recording medium

ABSTRACT

A plurality of types of recording pulse control rules for which the recording pulse waveform is determined according to the information signals to be recorded are stored in advance in an optical disk. When recording to the optical disk, information is recorded using a recording pulse where, due to the focused laser beam, the temperature in the recording layer cools more rapidly at a second information recording layer closer to the side where light is incident than at a first information recording layer farther away from the side where light is incident.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical information recording mediahaving a plurality of information recording layers, and an opticalinformation recording method and optical information recording andreproducing devices for recording information thereon.

2. Description of the Related Art

Recent years have witnessed robust developments in optical disks capableof recording and reproducing information signals such as video and audiosignals. Among these, optical disks on which two information recordinglayers are deposited so as to double the recording capacity are alreadycommercially available as read-only DVDs (Digital Versatile Disks). Asmentioned in JP 54-130902A, for example, the front recording layer, seenfrom the side from which the light source is incident, of such opticaldisks having a plurality of information recording layers is madesemitransparent, so that a sufficient amount of light is allowed toreach the recording layers that are farther from the side from which thelight is incident.

Phase-change type optical disks are one type of optical disk mediacapable of high-density recording. Data are recorded on phase-changeoptical disks by focusing the laser light to a beam spot less than 1 μmin diameter and directing this laser light onto the revolving disk toheat and melt the recording film. The temperature that the recordingfilm reaches and how it cools differs depending on the intensity of therecording laser, and the recording film is phase changed betweencrystalline and amorphous states.

When the intensity of the laser light is high (referred to as the “peakpower level”), the recording film is heated above its melting point andmelted and subsequently cools quickly, thereby becoming amorphous. Whenthe laser light is medium intensity (referred to as the “bias powerlever”), the recording film is kept above the temperature at which itcrystallizes but below its melting point, and therefore it iscrystallized. Amorphous areas are called marks and crystallized areasare called spaces. The method of recording data by assigning informationto the length of the marks and spaces is called “mark-edge recording.”With phase-change optical disks, the recording film can be melted at thepeak power level to form marks, regardless of whether the recording filmis amorphous or crystalline, and therefore direct overwriting, where olddata are erased and new data are recorded simultaneously with a singlebeam spot, is possible.

Reproduction is carried out by irradiating a laser light weak enough notto cause the recording film to change phase and detecting the intensityof the reflected light by a photodetector. The material used for therecording film and how it is configured with the protection layer allowsthe reflectance of the amorphous mark portions to be significantlydifferent from the reflectance of the crystalline space portions, sothat the difference in the amount of light that is reflected by the markportions and the space portions can be detected to obtain signals forreproducing the data information.

Numerous proposals have been made for using such phase-change opticaldisks in the two-layer optical disks described above. For example, JP2000-311346A proposes to provide the laser light at an ideal recordingpower for each recording layer because the recording layers differ fromone another. In another proposal, JP 2000-260060A teaches a techniquefor adopting a crystallization promotion film and an optical enhancementfilm, so that a stable change between amorphous and crystalline statescan be generated so as to record information without employing areflective film on the front recording layer.

However, the prior art mentioned in JP 54-130902A primarily addressesread-only applications, and lacks sufficient investigation intorewritable media with light transmission, absorbance, and reflectanceproperties adequate for practical applications. The technology disclosedin JP 2000-311346A merely uses recording pulses having identicalpatterns with respect to a plurality of recording layers and optimizingthe peak power at each layer. Furthermore, with the technology that isdisclosed in JP 2000-260060A, there is the problem that the optical diskstructure becomes complex, and as a consequence additional manufacturingsteps are required.

The present invention was derived in light of the foregoing problems,and it is an object thereof to provide an optical information recordingmedium having a plurality of rewritable information recording layers andto which information signals can be favorably recorded, and a method anda device for favorably recording information signals on an opticalinformation recording medium.

SUMMARY OF THE INVENTION

In order to achieve the above object, an optical information recordingmethod according to the present invention is an optical informationrecording method in which information signals are recorded on an opticalinformation recording medium provided with N information recordinglayers (where N is an integer of 2 or more), each having a recordinglayer that is subject to a physical state change due to localtemperature changes caused by a focused light beam. The method includesa step of selecting a recording pulse control rule that corresponds toan information recording layer to be recorded from a plurality ofrecording pulse control rules for which recording pulse waveforms aredetermined respectively, and a step of recording information signals onthe recording layer of the optical information recording medium bymodulating an intensity of the light beam in correspondence with therecording pulse that is determined by the selected recording pulsecontrol rule. Of the N information recording layers, if a layer farthestfrom the side of incidence is regarded as a first information recordinglayer and layers progressively closer to the side of light incidence areregarded as second to N-th information recording layers, then therecording pulse control rule that is selected when recording to thesecond to the N-th information recording layers corresponds to arecording pulse waveform that, if employed for recording to informationrecording layers having identical thermal properties, results in atemperature change of the recording layer that is steeper during coolingthan the recording pulse control rule that is selected when recording tothe first information recording layer.

An optical information recording and reproducing device according to thepresent invention is an optical information recording and reproducingdevice for recording information signals on an optical informationrecording medium provided with N information recording layers (where Nis an integer of 2 or more) each having a recording layer that issubject to a change in its physical state due to local temperaturechanges caused by the focused light beam. The device is provided with arule selection portion for selecting, from a plurality of recordingpulse control rules for which recording pulse waveforms are determinedrespectively, a recording pulse control rule that corresponds to aninformation recording layer to be recorded, and an optical recordingportion for recording information signals on the recording layer of theoptical information recording medium by emitting a light beam, theintensity of which is modulated to correspond to the recording pulsethat is determined by the selected recording pulse control rule. Of theN information recording layers, if a layer farthest from the side oflight incidence is regarded as a first information recording layer andlayers progressively closer to the side of incidence are regarded assecond to N-th information recording layers, then when recording to thesecond to the N-th information recording layers, the rule selectionportion selects a recording pulse control rule that, if employed forrecording to information recording layers having identical thermalproperties, results in a temperature change of the recording layer dueto the focused light of the light beam that is steeper during coolingthan the recording pulse control rule that is selected when recording tothe first information recording layer.

An optical information recording medium according to the presentinvention is an optical information recording medium provided with Ninformation recording layers (where N is an integer of 2 or more) eachhaving a recording layer that is subject to a change in its physicalstate due to local temperature changes caused by focused light beam, andon which information signals are recorded by modulating an intensity ofthe laser beam. The medium is provided with a control data region inwhich information of recording pulse control rules which determine therecording pulse waveforms for modulating the light beam have been storedin advance, and of the N information recording layers, if a layerfarthest from the side of light incidence is regarded as a firstinformation recording layer and layers progressively closer to the sideof incidence are regarded as second to N-th information recordinglayers, then a recording pulse control rule employed for the second tothe N-th information recording layers, if employed for informationrecording layers having identical thermal properties, results in a morerapid temperature change in the recording layer due to the focused lightof the light beam during cooling than the recording pulse control rulethat is employed for the first information recording layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of an optical diskdevice employing an optical information recording and reproducing methodaccording to an embodiment of the invention.

FIG. 2 is a cross-sectional view taken in the radial direction, whichschematically shows the layered structure of an optical disk used in anembodiment of the invention.

FIG. 3 is a diagram illustrating the recording pulse control rules forrecording pulses in an embodiment of the invention.

FIG. 4 is a waveform diagram showing other examples of recording pulsewaveforms according to an embodiment of the invention.

FIG. 5 is a waveform diagram showing other examples of recording pulsewaveforms according to an embodiment of the invention.

FIG. 6 is a cross-sectional view taken in the radial direction, whichschematically shows the layered configuration of an optical diskemployed in an embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention are described indetail with reference to the accompanying drawings. The followingembodiment is described using as the optical information recordingmedium an optical disk having two information recording layers andemploying a phase-change type recording material, where recording isperformed by changing the effective reflectance.

FIG. 1 shows the configuration of an optical disk device according to anembodiment of the present invention. An optical disk device 19 recordsand reproduces information using an optical disk 1. The optical disk 1is provided with a first information recording layer 21 and a secondinformation recording layer 23. Information tracks are formed in eachinformation recording layer. Data are recorded and reproduced throughthe irradiation of a laser from an optical head 4.

The optical disk device 19 is provided with the optical head 4, areproduction amplifier 5, a reproduction signal processing circuit 6, afocus control circuit 7, a tracking control circuit 8, a systemcontroller 9, a recording signal processing circuit 10, a pulse settingcircuit 11, and a laser drive circuit 12.

The optical head 4 irradiates a laser light at reproduction intensityonto the first or the second information recording layer of the opticaldisk 1 by way of a semiconductor laser and an objective lens not shownin the drawings. The optical head 4 also receives laser light that hasbeen reflected from the optical disk 1.

The reproduction amplifier 5 amplifies light detection signals that areoutput from the optical head 4 and outputs these as reproductionsignals. The reproduction signal processing circuit 6 for examplewaveform equalizes, binarizes, synchronizes, demodulates, and decodesthe reproduction signals that it receives from the reproductionamplifier 5 and either outputs these to an external host computer 14 asdigital data such as video, audio, or computer data, or outputs thesesignals to the outside as analog video/audio signals via a DA converternot shown in the drawings.

The focus control circuit 7 controls the position of the spot of thelaser that is irradiated from the optical head 4 onto the firstinformation recording layer 21 or the second information recording layer23, and the tracking control circuit 8 controls the position of the spoton the information tracks.

The information signal processing circuit 10 receives data to berecorded such as video, audio, or computer data from the host computer14, encodes and modulates the data, and then outputs the data asbinarized data. The pulse setting circuit 11 converts the binarized datainto recording pulses in correspondence with a preferable conversionrule and outputs the recording pulses. The laser drive circuit 12outputs a drive current to the semiconductor laser of the optical head 4based on the recording pulses that are received, so that the opticalhead 4 emits laser light at the intensity for recording.

The system controller 9 obtains address information indicating thecurrent position of the laser spot from the reproduction data that areoutput by the reproduction signal processing circuit, and also outputscontrol signals to the focus control circuit 7 and the tracking controlcircuit 8 so as to position the laser spot onto the information track ofa desired information layer. The system controller 9 also outputs acontrol signal to the laser drive circuit 12 so that the optical head 4irradiates laser light at the light intensity for reproducing or forrecording. Additionally, the system controller 9 outputs a controlsignal to the pulse setting circuit 11 so that the pulse setting circuit11 selects different modulation rules to correspond to the type ofinformation recording layer.

The host computer 14 is external to the optical disk device 19, andinputs/outputs information signals and control data such as digitalvideo and audio data and computer data.

FIG. 2 is a cross-sectional view in the radial direction schematicallyshowing the layered structure of the optical disk 1 that is employed inan embodiment of the present invention. The optical disk has beenprovided with two information recording layers. As shown in the drawing,the optical disk includes a first information recording layer 21, anoptical separation layer 22, a second information recording layer 23,and an optical transmission layer 24 sequentially deposited onto asupport substrate 20. The two information recording layers 21 and 23,with the optical separation layer 22 provided interposed between them,are each made of a plurality of optical thin films. Information isrecorded onto the information recording layers 21 and 23.

The first information recording layer 21 is provided by sequentiallydepositing a first reflective layer 25, a protection layer 26, aninterface layer 27, a first recording layer 28, an interface layer 29,and a protection layer 30. The second information recording layer 23 isprovided by sequentially depositing a second reflective layer 31, aprotection layer 32, an interface layer 33, a second recording layer 34,an interface layer 35, and a protection layer 36. The laser light forrecording and reproducing is incident from the side of the opticaltransmission layer 24.

The support substrate 20 is made of polycarbonate, a resin sheet such asPMMA, a UV curable resin, a glass substrate, or inorganic materials. Onthe surface of the substrate, continuous grooves (guide grooves, tracks)are formed in spirals or concentric circles. After the first informationrecording layer 21 is formed on the support substrate 20, the opticalseparation layer 22 having a surface covered by spiral or concentriccircle-shaped continuous grooves (guide grooves, tracks) is formedthrough a 2 P method, and the second information recording layer 23 isformed on the optical separation layer 22. The optical transmissionlayer 24 is then provided through spin coating or as a resin sheet, forexample.

The material for the protection layers 26, 30, 32, and 36 is preferablyboth physically and chemically stable, that is, having a melting pointand a softening temperature that are higher than those of the materialthat is adopted for the first recording layer 28 and the secondrecording layer 34, and does not form a solid solution with the materialof the recording layers. The protection layers may be made of adielectric such as Al₂O₃, SiO_(x), Ta₂O₅, MoO₃, WO₃, ZrO₂, ZnS, AlN_(x),BN, SiN_(x), TiN, ZrN, PbF₂, or MgF₂, or a suitable combination thereofAlso, the protection layers 26 and 30 and the protection layers 32 and36 can be formed of different materials, with the benefit that there isan increased degree of freedom in the thermal and optical disk design.Of course, they also can be formed of the same material.

The interface layers 27, 29, 33, and 35 are thin films of nitride orcarbide that are provided in order to inhibit diffusion between theelements constituting the layers adjacent thereto, and are for examplemade of a material that can be expressed by the general formula X—N orX—O—N. Although it is preferable that X is a component including atleast one element from Ge, Cr, Si, Al, and Te, this is not essential. Byproviding these interface layers, the elements constituting the firstand/or second recording layers 28 and 34 are kept from diffusing intothe elements constituting the protection layers 26, 30, 32, and 36,which are dielectric layers, and thus the ability to repeatedly recordand erase is improved. The effects of interface layers are described indetail in JP 04-52188A, for example.

The material of the first recording layer 28 and the second recordinglayer 34 can be a substance that experiences a structural change betweencrystalline and amorphous states, and for example can be a phase-changematerial incorporating Te, In or Se as a primary component. Primarycomponents of phase-change materials well known in the art includeTe—Sb—Ge, Te—Ge, Te—Ge—Sn, Te—Ge—Sn—Au, Sb—Se, Sb—Te, Sb—Se—Te, In—Te,In—Se, In—Se—Te, In—Sb, In—Sb—Se, and In—Se—Te. The first and secondrecording layers 28 and 34 ordinarily are formed in an amorphous state,and when they absorb energy such as a laser light they becomecrystalline, and as a result their optical constants (refractive indexn, attenuation coefficient k) are changed.

The optical separation layer 22 is an intermediate layer that isdisposed between the first information recording layer 21 and the secondinformation recording layer 23, and is provided such that when the firstinformation recording layer or the second information recording layerare reproduced, it diminishes the effects of reproduction signals fromthe other information layer to the extent that they can be ignored. Thethickness of the optical separation layer 22 is ordinarily not less than10μm and not more than 50μm, and is preferably not less than 20μm andnot more than 40μm. The material employed for the optical separationlayer 22 can be a material that is transparent with respect to thewavelength of the laser light that is irradiated to the firstinformation recording layer 21 in order to record or reproduce signals.The material of the optical separation layer 22 for example can be anepoxy-based UV curable resin or a sheet-shaped double-sided adhesivetape for adhering to the optical disk.

The first reflective layer 25 and the second reflective layer 31 may bemade of a metallic element such as Au, Al, Ni, Fe, Cr, or Ag, or analloy thereof. The function of the first reflective layer 25 is toincrease the efficiency of light absorption with the first recordinglayer 28, and thus is preferably provided. Although it is preferablethat the second reflective layer 31 is provided in order to ensure theamount of light for reproducing signals of the second informationrecording layer 23, it also must pass a portion of the laser light toenable recording and reproducing with respect to the first informationrecording layer 21. The second reflective layer 31 can be omitted, butif it is not provided, then the material and the thickness of theremaining layers of the second information recording layer 23 must beselected so that an adequate amount of reflected light can be obtainedfrom the second information recording layer 23.

The aforementioned first recording layer 28, the second recording layer34, the protection layers 26, 30, 32, and 36, the interface layers 27,29, 33, and 35, the first reflective layer 25, and the second reflectivelayer 31, for example, are each normally formed through electron beamdeposition, sputtering, ion plating, CVD, or laser sputtering.

Next, once again referring to FIG. 1, the operation of the optical diskdevice 19 configured as above shall be described.

First, when the optical disk 1 has been loaded, the host computer 14sends a command indicating the reproduction mode to the systemcontroller 9. The system controller 9 outputs control signals incorrespondence with the reproduction mode command to a spindle motorthat is not shown, the focus control circuit 7, the tracking controlcircuit 8, and the laser drive circuit 12. Once the spindle motor hasbegun revolving the optical disk 1, the laser drive circuit 12 is putinto reproduction mode and irradiates laser light at a constantreproduction power level from the optical head 4. The system controller9 sends a control signal to a transfer motor not shown in the drawings,which moves the optical head 4 in the radial direction of the disk sothat the beam spot falls onto the control data region of the opticaldisk 1.

Next, position control of the focus direction of the beam spot isperformed. In correspondence with a control signal from the systemcontroller 9, the focus control circuit 7 selects either the first orthe second information recording layer and moves the beam spot onto thatinformation control layer. Then, the tracking control circuit 8 controlsthe position in the disk radial direction (tracking direction). Thecontrol for positioning the beam spot in the focus direction is achievedthrough common focus control method such as astigmatism method and thecontrol for positioning the beam spot in the tracking direction isachieved through common tracking control method such as push-pullmethod, and thus a description of these control processes is omitted.These controls allow the beam spot to follow the information track.

Recording pulse control rule information regarding the ideal recordingpulse waveform for each information recording layer is stored in thecontrol data region in advance as depressed pits, meandering guidegrooves, or amorphous recording marks, and the laser light modulated bythese is returned to the optical head 4. The recording pulse controlrules are rules for which at least one of the number, height, width, andoutput timing of the recording pulses have been determined in order towrite recording mark of a predetermined length to the information trackaccording to the length of the period of continuous 1 bits or 0 bits ofthe binarized data to be recorded. The recording pulse control rulesalso are called the recording strategy. The recording pulse control ruleinformation stored in the control data region of each informationrecording layer may be a recording pulse control rule per se suitablefor the information recording layer, or alternatively, may be a numberor the like for identify the recording pulse control rule suitable forthe information recording layer. In the latter case, numbered recordingpulse control rules are stored in the optical disk device 19 beforehand,and upon recording, a recording pulse control rule corresponding torecording pulse control rule information read from the control dataregion of the target information recording layer is selected from therecording pulse control rules stored in the optical disk device 19. Inthe control data region of each information recording layer, informationof at least one recording pulse control rule suitable for the recordingto the information recording layer may be stored.

The laser light that is modulated and returned from the optical disk 1is received by the optical detector of the optical head 4 and convertedinto electrical signals. These signals are amplified by the reproductionamplifier 5 and then output to the reproduction signal processingcircuit 6 as reproduction signals. The reproduction signal processingcircuit 6 waveform equalizes, binarizes, synchronizes, demodulates, anddecodes, for example, the analog reproduction signals to extract thecontrol data, and then outputs the data to the system controller 9. Thesystem controller 9 reads the above-described recording pulse controlrules from a semiconductor memory or the like based on the control datathat are obtained, and transmits information pertaining to the recordingpulse control rules to the pulse setting circuit 11.

Here, the recording pulse control rules according to this embodiment aredescribed with reference to FIG. 3. In FIG. 3, (a) is a waveform diagramshowing the record data that are input to the pulse setting circuit 11as binary values, with the binary values indicating a high level and alow level. As described later, the period of the high level is expressedon the disk by marks and the period of the low level is expressed byspaces. In FIG. 3, (b) is a waveform diagram of the recording pulsesthat are output by the pulse setting circuit 11, and a single recordingmark corresponds to one short pulse or a sequence of a plurality ofshort pulses. The period during a space is held at the levelcorresponding to the intensity Pb (the “bias power”). Next, of the pulsecolumns corresponding to each mark, the initial pulse at the intensityPp (the “peak power”) is called the first pulse, the remainingcomb-shaped pulses (power Pp) are called sub-pulses, and the pulse atintensity Pc (the “cooling power”) following the final sub-pulse iscalled the cooling pulse. The period between sub-pulses is maintained ata power intensity Pbo (the “bottom power level”), and here this isequivalent to the bias power Pb. In FIG. 3, (c) shows the recordingmarks formed in the recording layer, seen from above.

In FIG. 3, the left side (A) shows a case where information signals arerecorded onto the first information recording layer, and the right side(B) shows a case where information signals are recorded onto the secondinformation recording layer. The recording pulse control rules forrecording the same binalized data are different in each case, andcompared to the former case, the emission waveform of the latter case issuch that, during recording, the material of the recording layer isheated to elevated temperatures by the laser light and then rapidlydrops in temperature. That is, at (b) of FIG. 3, in the waveform on theleft, the emission intensity is switched and changed between the biaspower (Pb) and the peak power (Pp), which is higher than Pb, whereas inthe waveform on the right side, an emission period at the cooling power(Pc), which is even lower than Pb, is added to the end of the firstpulse or short pulses sequence. This pulse is called a cooling pulse.Thus, because the emission power drops down to the intensity Pcimmediately after the intensity Pp, the drop in temperature from thehigh temperature state occurs more rapidly than in the case of thewaveform on the left, which drops only as far as the power Pb.

The reason the recording pulse control rules differ in this way isdescribed below. With optical disks having a plurality of informationrecording layers, it is imperative that the front information recordinglayer, seen from the side from which the laser light is incident, ismade semitransparent so that light reaches the rear informationrecording layer. For that reason, the reflection layer or the recordinglayer of the front information recording layer ordinarily must be thinor removed. However, the reflective layer not only reflects laser lightbut also serves as a heat sink for rapidly returning a recording layerelevated in temperature to its normal temperature. Thus, if thereflective layer is thin or removed, then the heat-diffusion propertiesof the entire information recording layer are diminished. On the otherhand, the rear information recording layer does not have to besemitransparent, and thus its reflective layer can be provided thick,and the heat-diffusing effect can be sufficiently increased. For thatreason, in this embodiment, different recording pulse control rules areprovided for the first information recording layer and the secondinformation recording layer, and the light intensity immediately afterthe Pp pulse in the latter case can be significantly reduced over thatof the former case. Consequently, the low heat-diffusion properties ofthe second information recording layer are compensated for and thecooling speed during recording is substantially equivalent in bothcases, so that even if an identical recording layer material or layerstructure is adopted, similar recording marks can be formed in eitherinformation recording layer. The emission intensity Pc can be determinedin advance by taking into consideration the cooling speed that isrequired to form the recording marks and the heat-diffusion property ofthe second information recording layer 23.

Here, the operation of the optical disk device 19 for recordinginformation to an information recording layer of the optical disk 1 isexplained. The system controller 9 moves the optical head 4 so that thebeam spot falls onto the track of the test write region in the targetinformation recording layer of the optical disk 1. Next, the systemcontroller 9 sends control signals to the recording signal processingcircuit 10 and the pulse setting circuit 11 so that the test patterndata for test write in a learning process are output. Based on the drivepulse from the laser drive circuit 12, the optical head 4 emits laserlight that has been modulated between the power levels and records marksonto the disk corresponding to the test pattern. When recording of thetest pattern has finished, the system controller 9 shifts to thereproducing mode and sends control signals to the laser drive circuit 12so that the intensity of the laser light that is emitted by the opticalhead 4 is dropped down to the reproduction power level. Then, theactuator of the optical head 4 is controlled so that the beam spotreturns to the position where the test pattern has been recorded. Thelaser light that is emitted is modulated in accordance with the testpattern and then returned to the optical head 4, where it is received bythe light detector and output as reproduction signals. The reproductionsignal processing circuit 6 then waveform equalizes, binarizes,synchronizes, demodulates, and decodes, for example, the reproductionsignals amplified by the reproduction amplifier 5. At the same time, thereproduction signal processing circuit 6 measures the modulation, theerror rate, the synchronization jitter, or the edge shift, for example,of the reproduction signals. The test pattern is repeatedly recorded andreproduced as above while changing the emission intensity Pp and Pb, andwhen the modulation, the error rate or the jitter falls below apreferred threshold value, the system controller 9 ends the learningprocess.

In the learning process described above, when a test write is performedfor the first time in a learning process of each information recordinglayer, the pulse setting circuit 11 employs a recording pulse controlrule selected according to recording pulse control rule information readfrom the control data region of the foregoing information recordinglayer. During learning at the second information recording layer 23, arecording pulse control rule with which the recording layer is cooledmore rapidly than the first information recording layer 21 is chosen.Also, when the result of recording and learning at the secondinformation recording layer 23 is that the measured values such as themodulation, the error rate or the jitter fall outside the tolerancerange, then another recording pulse control rule with which more rapidcooling occurs is selected, and the learning process is performed onceagain, or learning can be repeated in order starting from the recordingpulse control rule with the most rapid cooling. Also, in learning, byalso subjecting the time parameters (Tp, Ts, etc.) to a learningprocess, such as by fine-tuning the edge positions of the recordingpulses in correspondence with the length of the target marks, thequality of the recording signals can be improved further. Additionally,the frequency properties can be optimized with a reproduction signalprocessing circuit such as an equalizer.

After the learning process has been performed to determine the intensityof the laser light for recording, a shift is made to the informationsignal recording mode. The system controller 9 notifies the recordingsignal processing circuit 10, the pulse setting circuit 11, and thelaser drive circuit 12 that the device is in the information signalrecording mode and moves the beam spot up to the information signalregion of the target information recording layer in the optical disk 1.When the control for positioning the beam spot is finished, informationsignals to be recorded that are output from the host computer 14, suchas information signals like digitized video or audio data or computerdata, are transmitted to the laser drive circuit 12 as multi-pulsemodulated data via the recording signal processing circuit 10 and thepulse setting circuit 11. Then, the laser drive circuit 12 drives theoptical head 4 to emit a laser light. Thus, recording marks ofappropriate lengths are recorded onto the optical disk 1.

On the other hand, the information signals are reproduced as follows.The laser light projected to the optical disk 1 is modulated by therecording marks and returns to the optical head 4, and then istransmitted to the reproduction signal processing circuit 6 via thereproduction amplifier 5. The reproduction signal control circuit 6performs waveform equalization, binarization, synchronization,demodulatation, and error correction, and outputs the laser lightsignals to the host computer 14 as reproduction data.

Next, the device of FIG. 1 was used to record information signals on theoptical disk of FIG. 2 and then reproduce those signals. A GaN-basedsemiconductor laser with a 400 nm wavelength was used as the laser lightfor recording and reproducing, and the objective lens of the opticalhead 4 was given an NA of 0.85. The information signals were modulatedby 8-16, RLL (2, 10) modulation and recorded. Jitter was measured bybinarizing the reproduction signals and then measuring the differencebetween these and the clock signals of the reproduction PLL, and theratio of jitter to the standard clock period T was expressed in percent.Jitter was measured using the TA 520 made by Yokogawa ElectricCorporation. The permissible value of jitter in the DVD standard is 9%or less, for example, and the present embodiment adopts this value asthe standard permissible jitter value. The standard clock period T wasset to 13.6 nsec, the recording and reproducing linear velocity was setto 5.0 m/s, and the shortest recording mark pitch was set to 0.20 μm.The optical disk 1 was fabricated as follows. A polycarbonate substratewith a 120 mm diameter and 1.1 mm thickness was adopted for the supportsubstrate 20, and spiral shaped grooves with a 0.22 μm width, a 0.32 μmpitch, and a 22 nm depth were formed in the surface of the supportsubstrate 20. The first information recording layer 21 was formed on thesurface of the support substrate 20 by sequentially forming a 100 nmfirst reflective layer 25 made of AgPdCu, a 15 nm protection layer 26made of ZnS—SiO₂, a 5 nm interface layer 27 made of GeN, a 12 nm firstrecording layer 28 made of GeSbTe, a 5 nm interface layer 29 made ofGeN, and a 60 nm protection layer 30 made of ZnS—SiO₂. Next, the firstrecording layer 28 was initialized by irradiating it with a laser lightto change it from an amorphous state into a crystalline state, afterwhich the optical separation layer 22 was formed. The surfaces of theoptical separation layer 22 was of identical groove-shape with thesupport substrate 20 by a stamping. Then, the second informationrecording layer 23 was formed by sequentially forming a 6 nm secondreflective layer 31 made of AgPdCu, a 12 nm protection layer 32 made ofZnS—SiO₂, a 5 nm interface layer 33 made of GeN, a 6 nm second recordinglayer 34 made of GeSbTe, a 5 nm interface layer 35 made of GeN, and a 45nm protection layer 36 made of ZnS—SiO₂. After the second informationrecording layer 23 was formed, the second recording layer 34 wasirradiated by a laser light to change it from an amorphous to acrystalline state and initialize it. Finally, an optical transmissionlayer 24 made of polycarbonate was adhered using a UV curable resin. Thecombined thickness of the adhered portion and the optical transmissionlayer 24 was set to 85 μm and the thickness of the optical separationlayer 22 was set to 30 μm. With the optical disk 1 according to thisembodiment, signals can be rewritten to the first and second informationrecording layers 21, 23 at a Pp, Pb, and Pc of approximately 10, 4, and4 mW and 8, 4, and 0.6 mW, respectively, and the reproduction power wasapproximately 0.6 mW. The optical disk configured as above has anapproximately 20% reflectance at the first information recording layer21 and an approximately 6% reflectance and an approximately 50%transmittance at the second information layer 23, which was favorable.Thus, the effective reflectivity of the first information recordinglayer through the second information recording layer was approximately5%.

Table 1 shows the measured values of reproduction signal jitter for eachinformation reproduction layer when information signals are recorded andreproduced under the above conditions. For the second informationrecording layer 23, a jitter of less than 9% could not be obtained whenthe recording waveform A shown in FIG. 3 was adopted, but a favorablejitter value of less than 9% was obtained when the recording waveform Bwas adopted. In contrast, for the first information recording layer 21,jitter less than 9% was obtained when the recording waveform A wasadopted, but a jitter value higher than 9% was found when the recordingwaveform B was adopted. TABLE 1 First Information Second InformationRecording Layer Recording Layer Recording Waveform 8.8% 11.5% ARecording Waveform 9.5% 8.9% B

FIGS. 4 and 5 are waveform diagrams illustrating other examples ofrecording pulse waveforms in this embodiment of the present invention.In these drawings, (a) shows the recording pulse corresponding to theshortest recording mark, and (b) shows the recording pulse correspondingto a relatively long recording mark. The examples C to I are eachrecording pulses based on different recording pulse control rules. Theserecording pulses have been designed so that in all cases cooling occursmore rapidly than with the recording pulse A shown in FIG. 3 when usedwith respect to the second information recording layer 23.

First, the waveform C is a waveform in which the power betweensub-pulses of the recording pulse waveform B of FIG. 3 is dropped to Pc,which is lower than the bias power level Pb, so as to achieve more rapidcooling than the waveform B. Here, the length (time) of the first pulseand the cooling pulse are Tp and Tc, respectively, and the length (time)of the sub-pulse and the period between sub-pulses are Ts and Tb,respectively. The laser irradiation intensity, that is, the pulseheight, is Pp1 at the first pulse and the sub-pulses, Pc at the coolingpulse and the period between sub-pulses, and Pb at other periods. In thewaveform D, Tp and Ts are shorter than in the recording pulse waveform Aof FIG. 3, and the pulse height Pp2 is higher than the peak power levelPp1 of the waveform A. Here, Tb is longer than in waveform A, and thisboosts the cooling effect. Waveforms C and D were conceived so as toachieve a more rapid drop in temperature after the recording film ismelted than in the case of waveform A. Therefore, by using thesewaveforms for the second information recording layer 23 and using thewaveform A for the first information recording layer 21, informationsignals can be favorably recorded on either layer.

The waveform E of FIG. 4 has a longer Tc than the waveform C. Also, thewaveform F has a lower cooling pulse height Pc and bottom pulse heightPbo than the waveform C. The waveform G in FIG. 5 has a narrower firstpulse than the waveform C. The waveform H is identical to the waveform Gexcept that the length of the bottom pulse immediately after the firstpulse is longer. The waveform I is a waveform in which the periodbetween sub-pulses in the waveform D is dropped down to Pc and a coolingpulse has been added. All of the above waveforms E, F, G, H, and I coolthe recording film more rapidly than the waveform C. Consequently, thewaveform C can be adopted for the first information layer 21 and any ofthe waveforms E, F, G, H, or I can be adopted for the second informationrecording layer 23. Additionally, waveforms with different coolingeffects can be selected from these waveforms so that the pulse capableof more rapid cooling can be used with respect to the second informationrecording layer 23. In this case, a recording material or layerstructure with relatively low thermal conduction efficiency can beadopted for the first information recording layer 21 as well, and as aresult the degree of design freedom for the optical disk 1 is increased.

Table 2 shows an example of recording pulse control rule information tobe stored in the control data region of the optical disk 1. Table 2shows specific parameters of the recording pulses to be used for thefirst and second information recording layers 21, 23. In Table 2, Pp,Pb, Pc, Tp, Ts, Tb, and Tc are the same parameters as those appearing inFIGS. 3 to 5. The values of the Pp, Pb, and Pc columns indicate theheight of the recording pulse and are the power of the laser light inmW, whereas Tp, Ts, Th, and Tc indicate the width of the recording pulsein units of nsec. In Table 2, waveform A, that is, the recording pulsewaveform expressed by the parameters in the upper columns of the Table2, is adopted for the first information layer 21, and waveform B, thatis, the recording pulse waveform expressed by the parameters in thelower columns of the Table 2, is adopted for the second informationlayer 23. Table 3 shows other examples of recording pulse control ruleinformation. In Table 3, waveform G, that is, the recording pulsewaveform expressed by the parameters in the upper columns of the Table3, is adopted for the first information layer 21, and waveform I, thatis, the recording pulse waveform expressed by the parameters in theupper columns of the Table 3, is adopted for the second informationlayer 23. It should be noted that Tp, Ts, Tb, and Tc can be representedby not only the absolute values of the pulse width but also as amultiple of the standard clock period (for example, 1 T or 0.5 T).

Also, instead of numerically storing each parameter of the waveforms inthe control data region of the optical disk 1 as in the Tables 2 and 3,a unique number can be assigned to each recording pulse waveform, and bystoring information on which waveform corresponds to which number withina memory on the device side, it is possible to store only the waveformnumbers in the control data region of the optical disk 1. TABLE 2 Pp PbPc Tp Ts Tb Tc First Information Recording 10 4 4 13.6 6.8 6.8 0 LayerSecond Information Recording 10 4 0.6 13.6 6.8 6.8 13.6 Layer

TABLE 3 Pp Pb Pc Tp Ts Tb Tc First Information Recording Layer 10 4 0.66.8 6.8 6.8 6.8 Second Information Recording Layer 10 4 0.6 6.1 5.4 7.59.6

According to the above, in the present embodiment, the emission pulse ofthe laser is switched with respect to the two information recordinglayers so that the emission pulse with which cooling occurs more rapidlyis selected for the recording film of the second information recordinglayer, which has low heat diffusion properties, and as a result,recording marks can be favorably formed in an optical disk having twoinformation recording layers. Thus, the recording quality for two-layeroptical disks is improved.

It should be noted that the present embodiment was described with regardto an optical disk of a configuration where the thickness of thereflective layers is different for the first and the second informationrecording layers, as shown in FIG. 2. However, the present embodiment isof course not limited this configuration. For example, in order toincrease the transmittance of the second information recording layer 23,the second reflective layer 31 can be removed entirely, or the secondreflective layer 31 can have the same thickness but be madesemitransparent by changing the material thereof.

Additionally, the recording pulse control rules are not limited to thoseshown in FIGS. 3-5, and it is only necessary that there are tworecording pulse control rules and one of the rules obtains a recordingpulse waveform where the temperature within the recording layer fallsmore rapidly after its temperature has been increased to its meltingpoint than a waveform of the other rule. Additionally, although in theabove embodiments the recording pulse control rule for each informationrecording layer is stored in the control data region of each informationrecording layer, it is possible that the recording pulse control rulesfor all information recording layers are stored in the control dataregion of any one of the information recording layers. This ispreferable because the recording pulse control rules for all informationrecording layers can be obtained by one time access to the control dataregoin.

Further, the present embodiment was described using an optical diskprovided with two information recording layers, but the basic principleset forth in this embodiment remains the same when applied to an opticaldisk having three or more information recording layers. That is, if anoptical disk has three or more information recording layers, then thetransmissivity of all layers except for the one farthest from the sideof the optical disk on which the laser light is incident must be large.Consequently, as mentioned above, the reflective layers must be thin,which results in a drop in heat diffusivity. Thus, the recording pulsewaveforms can be chosen so that the recording pulse that is used for allinformation recording layers other than the one that is farthest fromthe side that the laser light is incident results in more rapid coolingthan the recording pulse that is employed for the farthest informationrecording layer from the side on which the laser is incident. By doingso, information signals can be recorded favorably with respect to allthe information recording layers.

As an example of the above, FIG. 6 shows an optical disk having fourinformation recording layers. In FIG. 6, a first information recordinglayer 21, a first optical separation layer 39, a second informationrecording layer 23, a second optical separation layer 40, a thirdinformation recording layer 41, a third optical separation layer 42, afourth information recording layer 43, and an optical transmission layer24 are deposited sequentially onto a support substrate 20. Each of thefour information recording layers 21, 23, 41, and 43, which are providedwith the optical separation layers 39, 40, and 42 interposed betweenthem, are made of a plurality of optical thin films. The firstinformation recording layer 21 is provided by sequentially depositing afirst reflective layer 25, a protection layer 26, an interface layer 27,a first recording layer 28, an interface layer 29, and a protectionlayer 30. The second information recording layer 23 is provided bysequentially depositing a second reflective layer 31, a protection layer32, an interface layer 33, a second recording layer 34, an interfacelayer 35, and a protection layer 36. The third information recordinglayer 41 is provided by sequentially depositing a third reflective layer44, a protection layer 45, an interface layer 46, a third recordinglayer 47, an interface layer 48, and a protection layer 49. The fourthinformation recording layer 43 is provided by sequentially depositing afourth reflective layer 50, a protection layer 51, an interface layer52, a fourth recording layer 53, an interface layer 54, and a protectionlayer 55. The laser light for recording and reproducing is incident fromthe optical transmission layer 24 side.

In the four-layer configuration shown in FIG. 6, the laser light mustpass through three information recording layers 42, 40, and 39 andbecome incident on the information recording layer 21 that is farthestfrom the side on which the laser light is incident. Therefore, it ispreferable that the transmissivity of the information recording layersbecomes progressively increased towards the front layers. Also, it ispreferable that a substantially equivalent amount of light is reflectedfrom each information recording layer. To that end, the informationrecording layers are designed so that the reflectance is progressivelyincreased towards the back layers. In the configuration shown in FIG. 2,the thickness of the second reflective layer 31 and the second recordinglayer 34 are both 6 nm, and in a conceivable configuration, one of thethird reflective layer 44 and the third recording layer 47 is made eventhinner in the third information recording layer 41, for example, thethird recording layer 47 is set to 3 nm, so as to increase thetransmissivity. Also, in another conceivable configuration, although thecooling properties are sacrificed, the third or fourth reflective layerscan be removed in order to increase the transmissivity. Thus, it ispreferable that the thickness of the reflective layers or recordinglayers becomes progressively thicker towards the back informationrecording layers and progressively thinner towards the front informationrecording layers. Consequently, the heat diffusivity progressively droptowards the front information recording layers, and thus sharperrecording pulses are used. As an example, in the waveform I, the pulsewidth Tp or Ts can be narrowed progressively toward the front layers orthe peak power Pp2 can be increased progressively toward the frontlayers. This leads to sharp changes in the light intensity duringrecording, and sufficient cooling speeds can be obtained in therecording layers even in the front information recording layers, so thatsufficiently large recording marks can be formed.

It should be noted that if the first information layer has the mostsignificant difference in thermal properties compared to the otherinformation recording layers and the thermal properties of the second,third, and fourth information recording layers do not significantlydiffer from one another, then to the extent that recording pulses withsteeper changes in laser light intensity are employed, it is of coursepossible to use substantially identical recording pulses for the otherthree information recording layers.

According to the present invention, the recording pulse control rulesare selected in correspondence with the information recording layers andthe recording pulse where cooling occurs most rapidly is selected forthe information recording layer(s) with low heat-diffusion properties,so that information signals can be favorably recorded on an opticalinformation recording medium having a plurality of information recordinglayers.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1. An optical information recording method in which information signalsare recorded on an optical information recording medium provided with Ninformation recording layers (where N is an integer of 2 or more) eachhaving a recording layer that is subject to a change in its physicalstate due to local temperature changes caused by a focused light beam,the method comprising: a step of selecting a recording pulse controlrule, from a plurality of recording pulse control rules for whichwaveforms of a recording pulse are determined respectively, incorrespondence with an information recording layer to be recorded, and astep of recording information signals on the recording layer bymodulating an intensity of the light beam in correspondence with therecording pulse that is determined by the selected recording pulsecontrol rule; wherein of the N information recording layers, if a layerfarthest from the side of light incidence is regarded as a firstinformation recording layer and layers progressively closer to the sideof light incidence are regarded as second to N-th information recordinglayers, then the recording pulse control rule that is selected whenrecording to the second to the N-th information recording layerscorresponds to a recording pulse waveform that, if employed forrecording to information recording layers having identical thermalproperties with the first information recording layer, results in asteeper temperature change in the recording layer during cooling thanthe recording pulse control rule that is selected when recording to thefirst information recording layer.
 2. The optical information recordingmethod according to claim 1, wherein the information signals areexpressed by a length of a mark period and a length of a space period onthe recording layer, and the recording pulse control rule determines atleast one of a number, height, width, and output timing of recordingpulses for recording marks of a predetermined length.
 3. The opticalinformation recording method according to claim 2, wherein markscorresponding to identical information signals are recorded insubstantially equivalent shapes at each information recording layer. 4.The optical information recording method according to claim 1, whereinthe recording layers of the optical information recording medium areformed by a phase-change type material that undergoes a change betweenamorphous and crystalline states.
 5. The optical information recordingmethod according to claim 1, wherein the second to the N-th informationrecording layers are formed by a semi-transparent material for the lightbeam.
 6. The optical information recording method according to claim 4,wherein at least one of the plurality of recording pulse control rulescorresponds to a recording pulse waveform to modulate the intensity ofthe light beams at the mark periods between a peak power levelsufficient to melt the recording layer, a bias power level sufficient tocrystallize the recording layer, and a cooling power level that is lowerthan the peak power level and the bias power level, and wherein thepulse corresponding to the cooling power level is located at leastimmediately after the pulse columns of the peak power level and the biaspower level.
 7. The optical information recording method according toclaim 6, wherein at least one of the plurality of recording pulsecontrol rules corresponds to a recording pulse waveform to modulate theintensity of the light beam at mark periods between the peak powerlevel, the bias power level, the cooling power level, and a bottom powerlevel, the bias power level, and the cooling power level, andalternately switch the intensity of the light beam between the peakpower level and the bottom power level in at least a portion of the markperiod.
 8. The optical information recording method according to claim6, wherein at least one of the recording pulse control rules that isselected when recording to the second to the N-th information recordinglayers corresponds to a recording pulse waveform having a cooling powerlevel period that is longer than the cooling power level period of therecording pulse waveform that is employed for the first informationrecording layer.
 9. The optical information recording method accordingto claim 6, wherein at least one of the recording pulse control rulesthat is selected when recording to the second to the N-th informationrecording layers corresponds to a recording pulse waveform having acooling power level that is lower than the cooling power level of therecording pulse waveform that is employed for the first informationrecording layer.
 10. The optical information recording method accordingto claim 7, wherein at least one of the recording pulse control rulesthat is selected when recording to the second to the N-th informationrecording layers corresponds to a recording pulse waveform where the sumof the length of the bottom power level periods is longer than the sumof the length of the bottom power level periods of the recording pulsewaveform that is employed for the first information recording layer. 11.The optical information recording method according to claim 7, whereinat least one of the recording pulse control rules that is selected whenrecording to the second to the N-th information recording layerscorresponds to a recording pulse waveform having a bottom power levelthat is lower than the bottom power level of the recording pulsewaveform that is employed for the first information recording layer. 12.The optical information recording method according to claim 6, whereinat least one of the recording pulse control rules that is selected whenrecording to the second to the N-th information recording layerscorresponds to a recording pulse waveform having a peak power levelperiod that is shorter than the peak power level period of the recordingpulse waveform that is employed for the first information recordinglayer.
 13. The optical information recording method according to claim7, wherein at least one of the recording pulse control rules that isselected when recording to the second to the N-th information recordinglayers corresponds to a recording pulse waveform having a plurality ofbottom power level periods with respect to a predetermined mark, and aninitial period of the plurality of bottom power level periods is longerthan an initial period of a bottom power level periods in a recordingpulse waveform that is employed when recording the predetermined mark tothe first information recording layer.
 14. The optical informationrecording method according to any one of claims 1 to 13, furthercomprising a learning step of determining an optimal light beamintensity for recording information signals to the information recordinglayers respectively, wherein when recording to the second to the N-thinformation recording layers, in the learning step, a recording pulsecontrol rule where the temperature change in the recording layer issteeper during cooling is selected with priority from the plurality ofrecording pulse control rules and a test write is performed incorrespondence with the selected recording pulse control rule.
 15. Anoptical information recording and reproducing device for recordinginformation signals on an optical information recording medium providedwith N information recording layers (where N is an integer of 2 or more)each having a recording layer that is subject to changes in its physicalstate due to local temperature changes caused by a focused light beam,the device comprising: a rule selection portion for selecting, from aplurality of recording pulse control rules for which recording pulsewaveforms are determined respectively, a recording pulse control rulethat corresponds to an information recording layer to be recorded, andan optical recording portion for recording information signals on therecording layer by emitting a light beam, the intensity of which ismodulated in correspondence with the recording pulse waveform that isdetermined by the selected recording pulse control rule; wherein of theN information recording layers, if a layer farthest from the side oflight incidence is regarded as a first information recording layer andlayers progressively closer to the side of light incidence are regardedas second to N-th information recording layers, then when recording tothe second to the N-th information recording layers, the rule selectionportion selects a recording pulse control rule that, if employed forrecording to information recording layers having identical thermalproperties with the first information recording layer, results in asteeper temperature change in the recording layer due to the focusedlight beam during cooling than the recording pulse control rule that isselected when recording to the first information recording layer. 16.The optical information recording and reproducing device according toclaim 15, wherein the information signals are expressed by a length of amark period and a length of a space period on the recording layer, andthe recording pulse control rule determines at least one of a number,height, width, and output timing of recording pulses for recording marksof a predetermined length.
 17. The optical information recording andreproducing device according to claim 16, wherein marks corresponding toidentical information signals are recorded in substantially equivalentshapes at each information recording layer.
 18. The optical informationrecording and reproducing device according to claim 15, wherein therecording layers of the optical information recording medium are formedby a phase-change type material that undergoes a change betweenamorphous and crystalline states.
 19. The optical information recordingand reproducing device according to claim 15, wherein the second to theN-th information recording layers of the optical information recordingmedium are formed by a semi-transparent for the light beam.
 20. Theoptical information recording and reproducing device according to claim18, wherein at least one of the plurality of recording pulse controlrules corresponds to a recording pulse waveform to modulate theintensity of the light beam at the mark periods between a peak powerlevel sufficient to melt the recording layer, a bias power levelsufficient to crystallize the recording layer, and a cooling power levelthat is lower than the peak power level and the bias power level, andwherein the pulse corresponding to the cooling power level is located atleast immediately after the pulse columns of the peak power level andthe bias power level.
 21. The optical information recording andreproducing device according to claim 20, wherein at least one of theplurality of recording pulse control rules corresponds to a recordingpulse waveform to modulate the intensity of the light beam at markperiods between the peak power level, the bias power level, the coolingpower level, and a bottom power level, and alternately switch theintensity of the light beam between the peak power level and the bottompower level in at least a portion of the mark periods.
 22. The opticalinformation recording and reproducing device according to claim 20,wherein at least one of the recording pulse control rules that isselected when recording to the second to the N-th information recordinglayers corresponds to a recording pulse waveform having a cooling powerlevel period that is longer than the cooling power level period of therecording pulse waveform that is employed for the first informationrecording layer.
 23. The optical information recording and reproducingdevice according to claim 20, wherein at least one of the recordingpulse control rules that is selected when recording to the second to theN-th information recording layers corresponds to a recording pulsewaveform having a cooling power level that is lower than the coolingpower level of the recording pulse waveform that is employed for thefirst information recording layer.
 24. The optical information recordingand reproducing device according to claim 21, wherein at least one ofthe recording pulse control rules that is selected when recording to thesecond to the N-th information recording layers corresponds to arecording pulse waveform where the sum of the length of the bottom powerlevel periods is longer than the sum of the length of the bottom powerlevel periods of the recording pulse waveform that is employed for thefirst information recording layer.
 25. The optical information recordingand reproducing device according to claim 21, wherein at least one ofthe recording pulse control rules that is selected when recording to thesecond to the N-th information recording layers corresponds to arecording pulse waveform having a bottom power level that is lower thanthe bottom power level of the recording pulse waveform that is employedfor the first information recording layer.
 26. The optical informationrecording and reproducing device according to claim 20, wherein at leastone of the recording pulse control rules that is selected when recordingto the second to the N-th information recording layers corresponds to arecording pulse waveform having a peak power level period that isshorter than the peak power level period of the recording pulse waveformthat is employed for the first information recording layer.
 27. Theoptical information recording and reproducing device according to claim21, wherein at least one of the recording pulse control rules that isselected when recording to the second to the N-th information recordinglayers corresponds to a recording pulse waveform having a plurality ofbottom power level periods with respect to a predetermined mark, and aninitial period of the plurality of bottom power level periods is longerthan an initial period of a bottom power level periods in a recordingpulse waveform that is employed when recording the predetermined mark tothe first information recording layer.
 28. The optical informationrecording and reproducing device according to claim 15 to 27, furthercomprising a learning portion of determining an ideal light beamintensity for recording information signals on the information recordinglayers respectively, wherein when recording to the second to the N-thinformation recording layers, in the learning step, a recording pulsecontrol rule where the temperature change in the recording layer issteeper during cooling is selected with priority from the plurality ofrecording pulse control rules and a test write is performed incorrespondence with the selected recording pulse control rule.
 29. Anoptical information recording medium provided with N informationrecording layers (where N is an integer of 2 or more) each having arecording layer that is subject to change in its physical state due tolocal temperature changes caused by focused light beam, and on whichinformation signals are recorded by modulating an intensity of the laserbeam, the medium comprising: a control data region in which informationof recording pulse control rules for determining recording pulsewaveforms for modulating the light beam are stored in advance; whereinof the N information recording layers, if a layer farthest from the sideof light incidence is regarded as a first information recording layerand layers progressively closer to the side of light incidence areregarded as second to N-th information recording layers, then arecording pulse control rule employed for the second to the N-thinformation recording layers, if employed for information recordinglayers having identical thermal properties with the first informationrecording layer, results in a more rapid temperature change in therecording layer due to the focused light of the light beam duringcooling than the recording pulse control rule that is employed for thefirst information recording layer.
 30. The optical information recordingmedium according to claim 29, wherein the information signals arerecorded on the recording layers as a length of a mark period and alength of a space period, and the recording pulse control rules arerules for which at least one of a number, height, width, and outputtiming of recording pulses for recording marks of a predetermined lengthis determined.
 31. The optical information recording medium according toclaim 29, wherein a phase-change material that undergoes a changebetween amorphous and crystalline states is adopted as a material of therecording layers.